<textarea id="editor1" cols="10" rows="10">
	&lt;script><iframe src=javascript:alert(1)></iframe>
</textarea>

<textarea id="editor2" cols="10" rows="10">
	&lt;script><iframe/src="javascript:alert(2)">
</textarea>

<textarea id="editor3" cols="10" rows="10">
	&lt;script>alert(3);
</textarea>

<script>
	CKEDITOR.replace( 'editor1' );
	CKEDITOR.replace( 'editor2' );
	CKEDITOR.replace( 'editor3', {
		extraAllowedContent: 'script'
	} );
</script>